RE: Multiple SUA SGs, sending for SSP from SGs

Ilie,

Multiple SG scenarios are overall a bit problematic -or better said require
some care and attention-. This is due to the fact that the SCCP layer for AS
is hosted on SG and if you have multiple SGs, you will have multiple copies
of the same SCCP instance which do not know about each others state -if they
knew, they would be part of the same SG-.

OTOH, for most practical cases, one prbably can survive. If we consider your
example, I would expect ASP to send ASPIA to both SGs, causing each ot them
to send SSP -probably only of them would receive SST  though-.

Maybe slightly more interesting scenario is, what happens if ASP looses
connectivity to only one SG? This would cause the subsystem to be available
in one SG and unavailable on the other one, not something we want to have.
OTOH, we should remember multihoming feature of SCTP and what it practically
means to us: SCTP multihoming provides network/NIC redundancy, i.e. loss of
association is an indication for host failure. So, in the scenario I
described if it is ASP which is down, both SGs will detect loss of
association. If it is one SG which is down, it won't be able to send SSP.

In any case, one should be careful with multi-SG scenarios.

    Thanks,
    Tolga


> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Ilie Glib
> Sent: Tuesday, January 10, 2006 1:30 PM
> To: SIGTRAN
> Subject: [Sigtran] Multiple SUA SGs, sending for SSP from SGs
>
>
> Hello Folks,
>
> Let's consider two SUA SGs which provide connectivity to an SSN
> in IP network.
> SUA RFC (section 5.1.2.3.) suggests sending an SSP from an SG when the
> AS serving the SSN goes inactive in the SG and I also assume in case
> the SG loses connectivity to the AS.
>
> 5.1.2.3.  Unsuccessful ASP Fail-over scenario
>
>      ASP-a1            ASP-a2                SG                  SEP
>    (Primary)           (Backup)
>        +-------------ASP Inactive------------->
>        <-----------ASP Inactive ACK-----------+
>        <--------------------NTFY (AS Pending)-+
>                          <--NTFY (AS Pending)-+
>              After some time elapses (i.e., timeout).
>                                               +--------SSP-------->
>                                               <--------SST--------+
>        <-------------------NTFY (AS Inactive)-+
>                          <-NTFY (AS Inactive)-+
>
>
>
> What shall be done in multiple SGs scenario when the SSN is allowed
> via another SG?
>
> Is this a realistic example?
>
> Thank you in advance
>
> --
> Ilie
>
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